SMA tumor patients typically develop postoperatively a contralateral akinesia with or without speech deficit ("SMA syndrome"), which often regresses within the first three months. The time to recovery however varies, and has previously been related to structural integrity of transcallosal connectivity of the SMA and of the Frontal Aslant Tract (FAT). Whether SMA tumor patients differ in structural connectivity (SC) already prior to surgical intervention is however unclear. We investigated diffusion-MRI based SC in SMA tumor patients preoperatively compared to healthy controls.
13 SMA tumor patients (10 gliomas/2 metastases/1 meningioma; 5 right-hemispheric; mean age 49±21 yrs), and 13 matched healthy controls (49±16 yrs) underwent diffusion-MRI preoperatively. Applying deterministic diffusion tractography, SC of the FAT, and of transcallosal SMA connectivity to the contralateral SMA (SMA-SMA), and to the contralateral primary motor cortex (SMA-M1) was analyzed. Normalized parameters evaluated for each tract were tract volume, number of fibers, tract length, as well as mean fractional anisotropy (FA), and mean-, radial-, and axial-diffusivity (MD, RD, AD), which were compared between patients and controls.
For FAT connectivity, patients showed a trend towards smaller tract volumes, with MD (p<.012) and AD (p<.010) being ipsilesionally increased only in patients. Transcallosal SMA-SMA connectivity did not significantly differ between groups, although the mean number of fibers appeared to be increased in some of the patients (Meanpatients=0.81+/-0.47; Meancontrols=0.56+/-0.34), which however did not reach significance due to the high variance. For SMA-M1 connectivity, tract volumes were reduced (p<.005), and fiber length of contralesional compared to ipsilesional SMA-M1 connections (p<.026), as well as AD (p<.019) were increased in patients.
Patients showed tumor-associated signs of ipsilesional and transcallosal microstructural white matter disintegration, but with a high variance in homologue transcallosal SMA connectivity. Variability in transcallosal connectivity might relate to differing abilities for bihemispheric or contralateral information processing. Longitudinal studies should evaluate, whether tumor-associated alterations of transcallosal connectivity impact on the postoperative functional outcome in SMA tumor patients